complex

American  

[kuhm-pleks, kom-pleks, kom-pleks] / kəmˈplɛks, ˈkɒm plɛks, ˈkɒm plɛks /

adjective

1. composed of many interconnected parts; compound; composite.

   a complex highway system.

2. characterized by a very complicated or involved arrangement of parts, units, etc..

   complex machinery.

   Antonyms:

   simple

3. so complicated or intricate as to be hard to understand or deal with.

   a complex problem.

   Synonyms:

   labyrinthine, tangled, knotty

   Antonyms:

   simple

4. Grammar.

   1. (of a word) consisting of two parts, at least one of which is a bound form, as childish, which consists of the word child and the bound form -ish.

   2. complex sentence.

5. Mathematics. pertaining to or using complex numbers.

   complex methods; complex vector space.

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noun

1. an intricate or complicated association or assemblage of related things, parts, units, etc..

   the entire complex of our educational system; an apartment complex.

   Synonyms:

   labyrinth, tangle, web, network

2. Psychology. a system of interrelated, emotion-charged ideas, feelings, memories, and impulses that is usually repressed and that gives rise to abnormal or pathological behavior.

3. a fixed idea; an obsessive notion.

4. Mathematics.

   1. an arbitrary set of elements of a group.

   2. a collection of simplexes having specified properties.

5. Also called coordination compound.  Chemistry. a compound in which independently existing molecules or ions of a nonmetal complexing agent form coordinate bonds with a metal atom or ion.

6. Biochemistry. an entity composed of molecules in which the constituents maintain much of their chemical identity.

   receptor-hormone complex, enzyme-substrate complex.

verb (used with object)

1. Chemistry. to form a complex with.

verb (used without object)

1. Chemistry. to form a complex.

complex British  

/ ˈkɒmplɛks /

adjective

1. made up of various interconnected parts; composite

2. (of thoughts, writing, etc) intricate or involved

3. grammar

   1. (of a word) containing at least one bound form

   2. (of a noun phrase) containing both a lexical noun and an embedded clause, as for example the italicized parts of the following sentence: I didn't know the man who served me

   3. (of a sentence) formed by subordination of one clause to another

4. maths of or involving one or more complex numbers

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noun

1. a whole made up of interconnected or related parts

   a building complex

2. psychoanal a group of emotional ideas or impulses that have been banished from the conscious mind but that continue to influence a person's behaviour

3. informal an obsession or excessive fear

   he's got a complex about cats

4. Also called: coordination compound.  a chemical compound in which molecules, groups, or ions are attached to a central metal atom, esp a transition metal atom, by coordinate bonds

5. any chemical compound in which one molecule is linked to another by a coordinate bond

Usage

Complex is sometimes wrongly used where complicated is meant. Complex is properly used to say only that something consists of several parts. It should not be used to say that, because something consists of many parts, it is difficult to understand or analyse

Other Word Forms

• complexly adverb
• complexness noun
• overcomplex adjective
• quasi-complex adjective
• quasi-complexly adverb
• supercomplex adjective
• uncomplex adjective
• uncomplexly adverb
• uncomplexness noun

Etymology

Origin of complex

First recorded in 1645–55; 1905–10 complex for def. 7; adjective from Latin complexus, past participle of complectī, complectere “to embrace, encompass, include,” equivalent to complect- ( complect ) + -tus past participle suffix; noun from Late Latin complexus “totality, complex” ( Latin: “inclusion, grasping, embrace”), equivalent to complect(ere) + -tus suffix of verb action; reanalysis of the Latin verb as “to intertwine (completely)” influenced sense of the adjective

Explanation

People who are really good at math can handle complex math problems. The rest of us are all set with simple stuff like the times tables. Use complex to refer to something that is not simple. Something complex has two or more related parts, or is not simple in its structure. As a noun, a complex is a group of units, often a group of buildings. The adjective is stressed on the second syllable, but the noun is stressed on the first syllable. Complex is from Latin complexus, from complecti "to encircle or embrace."

Example Sentences

Officials described the discussions as tense and complex, with negotiators struggling to bridge gaps over security guarantees, control of maritime access and broader regional concerns tied to Iran’s role.

From Salon • Apr. 12, 2026

A White Paper is an in-depth piece of research or report, sometimes undertaken by governments, into a complex issue.

From BBC • Apr. 12, 2026

These exchanges appear to have encouraged cultural growth, more complex social behavior, and innovations such as formal burials and the symbolic use of ochre for decoration.

From Science Daily • Apr. 12, 2026

Iran also has a highly fortified tunnel complex in the so-called Pickaxe Mountain, near the Natanz facility, where it could potentially do nuclear work out of reach of even the most powerful U.S. weapons.

From The Wall Street Journal • Apr. 12, 2026

The complex math that continuously ran through her head tended to make her socially awkward, but also let her identify patterns where everyone else saw chaos.

From "City Spies" by James Ponti

Related Words

• complicated
• convoluted
• disturbing
• intricate
• obscure
• perplexing
• sophisticated